Functional expression in mammalian cells of a full-length cDNA coding for the pp42/MAP kinase (p42mapk) protein.

We recently cloned from a mouse 3T3 cell cDNA library a cDNA with sequence similarity to the p42mapk protein and other members of the MAP kinase family. To determine with certainty which member of the family this clone encodes, we have expressed the cDNA in COS cells and characterized the protein product. When the pSV2MAP plasmid carrying the full-length clone was transfected into COS cells, a protein of 42,000 Da was expressed. This 42 kDa protein displayed chromatographic properties indistinguishable from the endogenous p42mapk, and could be separated from the closely related pp44. In addition, upon serum stimulation, the 42 kDa protein became tyrosine-phosphorylated and enzymatically active towards the substrate myelin basic protein. We conclude that this clone codes for a functional p42mapk protein kinase.     

Nuclear localization of the phosphatidylserine receptor protein via multiple nuclear localization signals

The interaction between phosphatidylserine and its receptor on phagocytic cells plays a critical role in the clearance of apoptotic bodies under normal physiological condition. A specific receptor for phosphatidylserine (PSR) has recently been identified by phage display and shown to mediate phosphatidylserine dependent phagocytosis. Here we show that the protein encoded by the PSR cDNA is localized in the nuclei through multiple nuclear localization signals. First, a fusion between PSR and GFP is localized in the nuclei of transfected cells, suggesting that PSR have intrinsic nuclear localization capability. Indeed, affinity-purified anti-PSR antibodies identified a 47 kDa protein species in cells transfected with untagged PSR and localized this protein in the nuclei by immunofluorescent confocal microscopy. In NIH3T3 cells, which express endogenous PSR mRNA, a similar 47 kDa species was detected and localized in the nuclei. Finally, multiple nuclear localization signals were identified in PSR sequence, each capable of targeting GFP to the nuclei. Together, these results suggest that PSR may serve a dual role both on the cell surface and in the nuclei.     

T cell-specific adapter protein inhibits T cell activation by modulating Lck activity

We previously reported the isolation of a cDNA encoding a T cell-specific adapter protein (TSAd). Its amino acid sequence contains an SH2 domain, tyrosines in protein binding motifs, and proline-rich regions. In this report we show that expression of TSAd is induced in normal peripheral blood T cells stimulated with anti-CD3 mAbs or anti-CD3 plus anti-CD28 mAbs. Overexpression of TSAd in Jurkat T cells interfered with TCR-mediated signaling by down-modulating anti-CD3/PMA-induced IL-2 promoter activity and anti-CD3 induced Ca2+ mobilization. The TCR-induced tyrosine phosphorylation of phospholipase C-gamma1, SH2-domain-containing leukocyte-specific phosphoprotein of 76kDa, and linker for activation of T cells was also reduced. Furthermore, TSAd inhibited Zap-70 recruitment to the CD3zeta-chains in a dose-dependent manner. Consistent with this, Lck kinase activity was reduced 3- to 4-fold in COS-7 cells transfected with both TSAd and Lck, indicating a regulatory effect of TSAd on Lck. In conclusion, our data strongly suggest an inhibitory role for TSAd in proximal T cell activation.     

Alternative Splicing of the Cytoplasmic Domain of Neural Cell Adhesion Molecule Alters Its Ability to Act as a Substrate for Neurite Outgrowth

A full-length cDNA encoding 180-kDa neural cell adhesion molecule (NCAM 180) has been transfected into mouse NIH-3T3 fibroblasts, and stable clones expressing the transgene have been isolated and characterised. Transfection was associated with the expression of a major protein band of 180 kDa and a minor related band of 140 kDa. Antibodies reactive exclusively with human NCAM immunoprecipitated both proteins but failed to coprecipitate any other proteins. The ability of transfected NCAM to stimulate neurite outgrowth was determined by culturing rat cerebellar neurons on top of confluent monolayers of parental 3T3 cells or clones of transfected 3T3 cells expressing either NCAM 140 or NCAM 180. The results show that NCAM 180 is less able to act as a substrate for neurite outgrowth than NCAM 140.     

Characterization of a cDNA clone, encoding a 70 kDa heat shock protein from the dermatophyte pathogen Trichophyton rubrum

Trichophyton rubrum is an anthropophilic fungus causing up to 90% of chronic cases of dermatophytosis. To characterize T. rubrum proteins at the molecular level, we established a cDNA library of this pathogen. Here we describe a recombinant cDNA clone identical to eukaryotic 70kDa heat-shock proteins (HSPs). Western blot analysis using an anti HSP70 monoclonal antibody detected a recombinant fusion protein in Escherichia coli transformed with the expression vector containing the cloned cDNA insert. Southern blot analysis of T. rubrum genomic DNA detected no other members of the HSP70 gene family. Further analysis revealed the presence of two introns within the ORF of the HSP70 gene. In Northern blot analysis, the cDNA clone was hybridized to a RNA species of about 3.5kb which was constitutively expressed by cells cultured at 27 degrees C and was strongly up-regulated after culture at 37 degrees C. In summary, we have cloned the first member of the HSP family of dermatophytes and characterized it as a member of the Dnak subfamily of 70kDa HSPs.     

Isolation of multiple mouse cDNAs with coding homology to Saccharomyces cerevisiae CDC25: identification of a region related to Bcr, Vav, Dbl and CDC24.

In Saccharomyces cerevisiae, the product of the CDC25 gene is an essential Ras activator that appears to function by stimulating guanine nucleotide exchange on Ras. Using the ability of a mouse cDNA expression library to complement yeast cells lacking functional CDC25, Martegani et al. have identified a 1.7 kb partial cDNA from a gene, designated CDC25Mm, with homology to CDC25. We have now screened a mouse brain cDNA library to identify full-length clones of CDC25Mm. This cloning has led to the isolation of six distinct full-length cDNAs, each of which appear to be derived from the CDC25Mm gene, since their 3' 2 kb appear to be identical and to encode the same 661 C-terminal amino acids. Three cDNAs are predicted to encode protein products of 666 or 667 amino acids. The other three cDNAs encode products that are 836, 1120 and 1260 amino acids, respectively. A 241 amino acid region near the N-terminus of the two largest products was found to have homology to a domain shared by Bcr, Vav, Dbl and CDC24. Polyclonal antibodies raised to a peptide encoded by all the cDNAs have identified at least two protein products in NIH3T3 fibroblasts. Their apparent molecular weights are 75 and 95 kDa, which correspond closely to those predicted to be encoded, respectively, by the two shorter classes of cDNAs. In NIH3T3, the 95 kDa form is much more abundant than the 75 kDa form, while PC-12 pheochromocytoma cells contain relatively high levels of the 75 kDa form. We conclude that CDC25Mm is a complex gene whose protein products are regulated in a tissue-specific manner.     

The murine homologue of the T lymphocyte antigen CD28. Molecular cloning and cell surface expression

The human T lymphocyte Ag CD28 (Tp44) is a homodimeric glycoprotein expressed on the surface of a majority of human peripheral T cells and thymocytes. Although exposure of T cells to anti-CD28 mAb does not activate T cells, stimulation of CD28 can synergize with signals transmitted through the TCR or other stimuli to augment proliferation and lymphokine production. We have used a portion of the human CD28 cDNA to isolate a homologous murine cDNA from an EL4 T lymphoma library. The murine clone has 61% nucleotide identity with the human cDNA. Both human and murine sequences exhibit homology with members of the Ig supergene family and CTLA-4, a T cell specific murine gene. Many characteristics of the human CD28 molecule are conserved within the putative murine CD28 polypeptide. The murine cDNA sequence encodes a polypeptide of 218 amino acids that has 68% identity with the human sequence. Both the murine and human molecules are integral membrane glycoproteins with hydrophobic signal peptide sequences and transmembrane region. All five potential N-linked glycosylation sites are conserved and six of the seven cysteine residues of the mouse protein are found in the human CD28 polypeptide. The murine cDNA is encoded by a single copy nonrearranging gene whose expression at the mRNA level is restricted to T cells. A rabbit antiserum was raised against a synthetic peptide corresponding to a hydrophilic portion of the translated murine cDNA sequence. This antiserum identifies an 80-kDa homodimer consisting of disulfide-bonded subunits of 40 kDa that is expressed on splenic T cells, thymocytes, and several T cell tumors, but not on B cells. deglycosylation studies indicate that four of the five N-linked glycosylation sites are used and that the mature core protein has a molecular mass of 25 kDa, close to that predicted by the cDNA sequence. Transfection of the murine cDNA into Chinese hamster ovary cells resulted in the expression of an 80-kDa dimeric molecule that was immunoprecipitated by the antipeptide antiserum. Taken together, these data provide strong support that we have identified the murine homologue of CD28.     

Identification of a transforming gene of human papillomavirus type 16.

Previously, we observed sequential two-step alteration, growth stimulation, and progression to a more malignant state in NIH 3T3 cells transfected by human papillomavirus type 16 (HPV-16) DNA. In this study, we prepared a cDNA library from RNA extracted from cells transfected with the HPV-16 DNA and isolated cDNA clones which had growth-stimulating activity. Analysis of these cDNA clones indicated that the E7 open reading frame alone is responsible for inducing both steps of this cell transformation.     

Modifications in the myogenic program induced by in vivo and in vitro aging

In this study, we have used high density cDNA arrays to assess age-related changes in gene expression in the myogenic program of human satellite cells and to elucidate modifications in differentiation capacity that could occur throughout in vitro cellular aging. We have screened a collection of 2016 clones from a human skeletal muscle 3'-end cDNA library in order to investigate variations in the myogenic program of myotubes formed by the differentiation of myoblasts of individuals with different ages (5 days old, 52 years old and 79 years old) and induced to differentiate at different stages of their lifespan (early proliferation, presenescence and senescence). Although our analysis has not been able to underline specific changes in the expression of genes encoding proteins involved in muscle structure and/or function, we have demonstrated an age-related induction of genes involved in stress response and a down-regulation of genes involved both in mitochondrial electron transport/ATP synthase and in glycolysis/TCA cycle. From this global approach of post-mitotic cell aging, we have identified 2 potential new markers of presenescence for human myotubes, both strongly linked to carbohydrate metabolism, which could be useful in developing therapeutic strategies.     

Cloning of cDNA for natural killer cell stimulatory factor, a heterodimeric cytokine with multiple biologic effects on T and natural killer cells.

Previously we have reported the purification and characterization of a novel cytokine from an EBV-transformed B cell line, RPMI 8866. This factor, termed natural killer cell stimulatory factor (NKSF), possessed pleiotropic activities including the induction of IFN-gamma from PBL, enhancement of cytotoxicity by NK cells, and stimulation of the proliferation of PBL. Purified NKSF was found to be a disulfide-linked heterodimeric protein composed of 35-kDa and 40-kDa subunits (p35 and p40). We now report the molecular cloning of cDNA for both subunits of NKSF from RPMI 8866 cellular RNA. The cDNA sequences indicate that both genes are novel, and Southern blot analysis confirmed that both cDNA are of human genomic origin. [35S]Methionine labeling indicated that cos-1 cells transfected with either p35 or p40 cDNA produced unique protein species of appropriate size. Methionine labeling of cos-1 cells cotransfected with p35 plus p40 cDNA yielded a broad band migrating between 70 and 90 kDa on a nonreducing gel. Reduction of this high molecular weight material yielded bands correlating with p35 and p40 gene products. Only culture supernatant from cotransfected cos-1 cells had a high level of NKSF biologic activity. That the high molecular weight material was responsible for this activity was indicated by the observation that biologic activity in the culture supernatant migrated at 70 to 90 kDa in a nonreducing gel. Furthermore, anti-p40 serum was able to block the biologic activities of both recombinant and natural NKSF, which indicates that it is a component of the active protein. In contrast, no activity could be detected in the supernatants of cos-1 cells transfected with p40 or p35 cDNA alone. The spectrum of biologic activity produced by cotransfected cos-1 cells was the same as NKSF purified to homogeneity from the RPMI 8866 cell line. A synergistic augmentation of some of these responses was found by the addition of IL-2 or the co-stimulators PHA or phorbol diester. The synergistic stimulation by NKSF plus IL-2 of T and NK function supports the possibility that these cytokines might prove useful in cancer therapy.     

Identification and molecular cloning of tactile. A novel human T cell activation antigen that is a member of the Ig gene superfamily.

We have identified and cloned cDNA for a novel cell-surface protein that we have named Tactile for T cell activation, increased late expression. It is expressed on normal T cell lines and clones, and some transformed T cells, but no other cultured cell lines tested. It is expressed at low levels on peripheral T cells and is strongly up-regulated after activation, peaking 6 to 9 days after the activating stimulus. It is also up-regulated on NK cells activated in allogeneic cultures. It is not found on peripheral B cells but is expressed at very low levels on activated B cells. Tactile-specific mAb immunoprecipitates a band of 160 kDa when reduced and bands of 240, 180, and 160 kDa nonreduced. Using an antiserum produced with affinity-purified Tactile protein to screen a lambda gt11 library, we have identified Tactile cDNA. Northern blot analysis shows an expression pattern similar to that of the protein and transfection of COS cells with the full-length 5.2-kb cDNA results in cell-surface expression. Comparison with the sequence databanks show that Tactile is a member of the immunoglobulin gene superfamily, with similarity to Drosophila amalgam, the melanoma Ag MUC-18, members of the carcinoembryonic Ag family, the poliovirus receptor, and the neural cell adhesion molecule. The deduced primary sequence encodes a protein with three Ig domains, a long serine/threonine/proline-rich region typical of an extensively O-glycosylated domain, a transmembrane domain, and a 45 residue cytoplasmic domain. These data suggest that Tactile may be involved in adhesive interactions of activated T and NK cells during the late phase of the immune response.     

VCP, the mammalian homolog of cdc48, is tyrosine phosphorylated in response to T cell antigen receptor activation.

Activation of T cells through the T cell antigen receptor (TCR) results in the rapid tyrosine phosphorylation of a number of cellular proteins, one of the earliest being a 100 kDa protein. We have sought to identify this 100 kDa substrate by partially purifying the protein by antiphosphotyrosine (APT) affinity purification, in order to obtain amino acid sequence data and, using this information, to isolate the cDNA clone encoding the molecule. We report here that the amino acid sequence data showed pp100 to be the murine equivalent of porcine valosin containing protein (VCP), a finding confirmed from the cloning and sequencing of the murine pp100 cDNA. Sequence analysis has shown VCP to be a member of a family of ATP binding, homo-oligomeric proteins, and the mammalian homolog of Saccharomyces cerevisiae cdc48p, a protein essential to the completion of mitosis in yeast. We also provide proof that both endogenous and expressed murine VCP are tyrosine phosphorylated in response to T cell activation. Thus we have identified a novel component of the TCR mediated tyrosine kinase activation pathway that may provide a link between TCR ligation and cell cycle control.     

35 kDa fragment of h-caldesmon conserves two consensus sequences of the tropomyosin-binding domain in troponin T

Using a tropomyosin-coupled affinity column, we have demonstrated a direct association between the chymotryptic 35 kDa fragment of h-caldesmon, which is located at the C-terminal of the parent molecule, and gizzard tropomyosin. We have subsequently determined the nucleotide sequence of cDNA clones encoding the 35 kDa fragment from the cDNA library prepared from chick embryo gizzards, and have deduced the amino acid sequence. Calculating from the predicted sequence, the 35 kDa fragment is composed of 306 amino acid residues. In agreement with the tropomyosin-binding ability, the 35 kDa fragment conserves two consensus sequences of the tropomyosin-binding domain in troponin T. These results suggest that the 35 kDa fragment of h-caldesmon, at least in part, has a common property to the striated muscle troponin T.     

Cloning and characterization of a novel T cell activation gene

We have used the technique of subtractive hybridization to identify a T cell gene selectively expressed during activation via the antigen-receptor pathway. This gene, termed TCA3 (for T cell activation) encodes a mRNA which is expressed following concanavalin A (Con A) activation of T cell clones at levels of approximately 1% total poly(A)-containing mRNA. The cDNA isolate, termed TCA3.0, is 512 bases in length excluding poly(A) and encodes a predicted 92-amino acid protein having the characteristics of a secreted polypeptide of approximately 69 amino acids. The genomic organizations of TCA3 was determined for two lambda phage clones and was found to be a single copy gene containing at least three exons dispersed over less than 4.7 kb. The temporal appearance of TCA3 mRNA in response to several activating agents was examined. It is not transcribed in response to interleukin 2 stimulation, but is transcribed in response to either antigen or Con A stimulation and can be detected as early as 1 hr poststimulation. Expression TCA3 in response to Con A is blocked by cyclosporin A treatment. The combined data suggest that TCA3 may represent a new lymphokine.     

Detection of Mouse Tyrosinase With a Monoclonal Antibody MAT-1 Against Human Tyrosinase

In this study we explored the possible application of MAT-1, which has been established as a monoclonal antibody against human tyrosinase, for detection of mouse tyrosinase. The MAT-1 reacted with B16 mouse melanoma cells, but not with tyrosinase-negative NIH-3T3 mouse fibroblasts. In western blot analysis of the large granule fraction (LGF) of B16 cells, MAT-1 detected a single protein of 80 kDa, whose size was close to that of human tyrosinase detected with MAT-1 in extracts of human melanocytes. Furthermore, the 80 kDa band that was detected with MAT-1 in the LGF of B16 cells was also detected by DOPA reaction. In order to confirm that the protein detected with MAT-1 is tyrosinase, a transient expression assay was carried out. When mouse tyrosinase or mouse tyrosinase-related protein 1, which shares high homology with human tyrosinase, was transiently expressed in tyrosinase-negative K1735 mouse melanoma cells by cDNA transfection, MAT-1 reacted only with the cells expressing mouse tyrosinase. These results indicate that MAT-1 specifically reacts with mouse tyrosinase.